JAKARTA -- Indonesia has leased two amphibious fire-fighting planes from Russia to help douse forest fires that have been spreading smoke across the region for months, an official said on Tuesday.

The smoke pollution originating from Indonesian areas on Sumatra and Borneo islands has been the worst since 1997-98 when dry conditions linked to El Nino weather pattern caused choking haze that cost the region billions of dollars in economic losses.

The planes leased by the national disaster agency, however, come at a time when conditions in the haze-hit regions including Singapore and Malaysia have generally improved following rains.

"They will be ready on Wednesday. They can take 12 tonnes of water. With their large capacity, they will not require many stops," said Sugeng Triutomo, head of the agency's disaster mitigation division.

"The pilots also come from Russia because we do not know how to operate them on such a short notice," he added.

Another official said 32 Russians, including technicians, would be involved in targeting areas on Sumatra and Borneo.

Triutomo said the first target would be parts of southern Sumatra where there were still 15 hotspots raging.

Indonesia's neighbours have grown increasingly frustrated over the fires, most of which are deliberately lit by farmers or by timber and palm oil plantation companies to clear land for cultivation.

Recent rains have helped improve the situation, although unless sustained will not necessarily quell the flames and smoke, particularly in peat land areas, where fires are notoriously difficult to douse.

Indonesia's annual six-month rainy season usually starts in October and reaches its peak in January. This year the rains only sporadically started in Sumatra last week, with weather agencies forecasting the area will get consistent rains next month.